According to the Washington Post, which first reported the news, hackers were able to access all messages and emails sent over the DNC system.
DNC Chairwoman Debbie Wasserman Schultz, D-Fla., said the intrusion was treated like the “serious” incident it is and has contacted cybersecurity company CrowdStrike to respond to the incident.
"The security of our system is critical to our operation and to the confidence of the campaigns and state parties we work with," Wasserman Schultz told ABC News today. "When we discovered the intrusion, we treated this like the serious incident it is and reached out to CrowdStrike immediately. Our team moved as quickly as possible to kick out the intruders and secure our network."
Dmitri Alperovitch, the co-founder of CrowdStrike, told ABC News in an interview today that the firm knows "definitively" that the DNC was hacked by "two separate Russian intelligence agencies."
One, they are confident is the GRU, Russia's military intelligence agency, and the second, they are "less confident in, but have reason to believe" is the Federal Security Service (or FSB), Russia’s security service, Alperovitch said. A Russian Embassy spokesman told the Washington Post that he had no knowledge of such intrusions.
The hackers were "looking for opposition research on Trump and his campaign" and "they did take opposition research on Trump," Alperovitch told ABC News.
When asked why, Alperovitch said because "like everyone else in the world, the Russian government is keenly interested in who is Mr. Trump, what his foreign policy will be and what his relationship with Russia would be like. Secondly, anything they can find that they can use against him should he be president would also be of interest.”
When asked if it’s likely Russia is trying to hack the Trump campaign directly for their information, Alperovitch said he doesn’t know, but that it’s “not out of the realm of possibility.”
“This also shows you espionage has now moved off the just physical realm of recruiting spies and getting information, it’s now through cyber means. This is a traditional target of Russian intelligence for 100 years but now doing it for cyber,” Alperovitch said referring to U.S. candidates and campaigns. “I would say this is not surprising at all, this is what intelligence agencies” want to get.
He said the DNC is “absolutely” safer now, explaining that CrowdStrike did a full remediation this weekend and “kicked out both adversaries.” He added that they installed software because they “expect for them to come back."
"Russian intelligence’s interest in the U.S. political system will not cease, it will only intensify and there will be ongoing attempts to hack into the network going forward," Alperovitch said.
ABC News has also learned that the FBI is investigating this case.
ABC News' Mike Levine contributed to this report.